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[OM] Calculating reproduction ratio with teleconverter

Subject: [OM] Calculating reproduction ratio with teleconverter
From: Andrew Dacey <adacey@xxxxxxxxx>
Date: Sun, 28 Aug 2005 13:57:18 -0300
Wow, an actual on-topic post that's not digital to boot, will wonders
never cease?

I'm wondering about how to go about calculating the reproduction ratio
when combining a macro lens with a teleconverter.

Specifically, I have a Tamron 90/2.5 macro (the 2nd version) which
goes to 1:2 on it's own. If I attach my Vivitar macro focusing
teleconverter that would take me to 1:1 (it's a 2x converter) right?
But, then I can also focus the converter to get extra extension. How
do I calculate what the total ratio would be? Do I calculate the total
extension and then multiply by 2 or is there another way to work this
out?

>From my math, the 90 goes to 1:2 so that's 45mm of extension. The
converter goes to 1:1.5 with a 50mm at infinity so that means you get
33mm of extension if my math is right. So does that mean I have a
total extension of 78mm for a total reproduction ratio of 1:1.76?

PS, yes I know you're not supposed to use decimals in a ratio but it's
more clear than saying the ratio is 25:44.
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